CIRCULATION OF THE BLOOD 145 



as the action of the organ is so plainly contraction, its 

 function is to propel the blood into the arteries. 



Nor are we the less to agree with Aristotle in regard to 

 the importance of the heart, or to question if it receives sense 

 and motion from the brain, blood from the liver, or whether 

 it be the origin of the veins and of the blood, and such like. 

 They who affirm these propositions overlook, or do not rightly 

 understand, the principal argument, to the effect that the 

 heart is the first part which exists, and that it contains within 

 itself blood, life, sensation, and motion, before either the 

 brain or the liver were created or had appeared distinctly, 

 or, at all events, before they could perform any function. 

 The heart, ready furnished with its proper organs of motion, 

 like a kind of internal creature, existed before the body. 

 The first to be formed, nature willed that it should after- 

 wards fashion, nourish, preserve, complete the entire animal, 

 as its work and dwelling-place: and as the prince in a king- 

 dom, in whose hands lie the chief and highest authority, 

 rules over all, the heart is the source and foundation from 

 which all power is derived, on which all power depends in 

 the animal body. 



Many things having reference to the arteries farther il- 

 lustrate and confirm this truth. Why does not the pulmo- 

 nary vein pulsate, seeing that it is numbered among the 

 arteries? Or wherefore is there a pulse in the pulmonary 

 artery? Because the pulse of the arteries is derived from 

 the impulse of the blood. Why does an artery differ so 

 much from a vein in the thickness and strength of its coats? 

 Because it sustains the shock of the impelling heart and 

 streaming blood. Hence, as perfect nature does nothing 

 in vain, and suffices under all circumstances, we find that 

 the nearer the arteries are to the heart, the more do they 

 differ from the veins in structure ; here they are both stronger 

 and more ligamentous, whilst in extreme parts of the body, 

 such as the feet and hands, the brain, the mesentery, and 

 the testicles, the two orders of vessels are so much alike 

 that it is impossible to distinguish between them with the 

 eye. Now this is for the following very sufficient reasons: 

 the more remote the vessels are from the heart, with so much 

 the less force are they distended by the stroke of the heart, 



